Nitrogen effect on negative fixed charges of Al₂O₃ passivation film in crystalline Si solar cells

We demonstrated the electrical evolution of the AlO, AlN, and AlON and the nitrogen (N) effect on negative fixed charges, which is responsible for the reduced positive charge traps of Al₂O₃ passivation films in crystalline Si solar cells. The AlO and AlN deposited by RF sputtering system were served as reference samples, and the AlON prepared by a nitrogen plasma exposure was served as controlled sample. The electrical properties of these samples were demonstrated through high-low (HL) capacitance-voltage (C-V) of metal-insulator-semiconductor (MIS) and photo-induced current transient spectroscopy (PICTS) to investigate interface and bulk defect states in the insulating films. 1MHz C-V curves of AlO, AlN, and AlON films, in which flatband voltage shifts (VFB) are around -0.55, -2.8 and 3.6 V, respectively. It reveals that the positive shift takes place as compared to the others and negative fixed charges are dominant in the AlON film. It was observed that defect states were decreased in the AlON film, and especially the defect state of 0.42 eV approximately disappeared. From the HL C-V measurement, the positive interface state was reduced in density from 2.15 × 10¹² to 1.26 × 10¹⁰ cm^-2. It is suggested that the dominant negative fixed charges in the AlON film result from the nitrogen effect and that nitrogen atoms in the AlON film take positive charge traps to be passivated.